Nice progress 
In kernel 5.1 we have:
In kernel 5.2 we have:
In kernel 5.3 we’ll have:
- arm64: dts: rockchip: add WiFi+BT support on ROCK Pi4 board
- arm64: dts: rockchip: Enable HDMI audio on Rock Pi
So, from 5.3 on these should work:
- HDMI Display
- Console
- MMC, EMMC
- USB 2.0, USB-3.0
- Ethernet
- Mali GPU Node
- Wifi and Bluetooth
- Audio over HDMI
Also, uboot has first support:
[U-Boot] rockchip: rk3399: Add Rock PI 4 support
and LPDDR4 support is sent to the mailing list.